The locale Lib — CLDR Plural Rules, UTC Date & Number Formatting, and Language Autonyms

42.1. Why does the locale lib exist? (Pure-Ridgun CLDR Internationalization)

In systems programming, C's setlocale() mutates process-wide global state across threads, while linking libicu adds tens of megabytes of C++ dependencies. The locale lib (src/main/ridgun/lib/locale.rg, domain LOCALE) brings deterministic Unicode CLDR 46 rules and Howard Hinnant's $O(1)$ civil calendar directly into pure Ridgun:

1. Dual-Mode CLDR Cardinal Plural Rules (.po-compatible 2-form default + strict CLDR 46 "many"): plural category, plural categories, and plural index provide the 2-form ["one", "other"] mode expected by Gettext .po catalogs for Western European locales (es, ca, gl, eu, en, pt, sv, it, de, nl), French 0/1 -> "one", 3-form Slavic rules (ru, uk, pl), 6-form Arabic rules (ar), and invariant East Asian rules (ja, zh, ko), while plural category cldr and plural categories cldr expose strict CLDR 46 "many" for exact millions (1000000, 2000000...) in es, ca, pt, it, and fr.
2. UTC Date & Datetime Formatting (format date, format datetime, month name, weekday name): converts Unix epoch seconds in $O(1)$ into short, medium, long, and full locale patterns.
3. Locale-Aware Integer & Decimal Formatting (format int, format decimal): thousands grouping and half-away-from-zero decimal rounding.
4. Native Language Autonyms (language name) & BCP-47 / POSIX Tag Normalization (normalize locale) with deterministic fallback to "en".

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42.2. Algebraic Data Types and Complete API Catalog of locale

type LocaleDatePatterns =
  ldp_short  : String
  ldp_medium : String
  ldp_long   : String
  ldp_full   : String

type LocaleSpec =
  loc_code          : String
  loc_autonym       : String
  loc_plural_family : String
  loc_thousands_sep : String
  loc_decimal_sep   : String
  loc_months_full   : [String]
  loc_months_short  : [String]
  loc_weekdays_full : [String]
  loc_weekdays_short: [String]
  loc_date_patterns : LocaleDatePatterns

#	Function / Signature (fn ::)	Return Type
1	fn :: loc ascii lower char Int	Int
2	fn :: loc tag base char String Int Int String Int	String
3	fn :: loc tag base loop String Int Int String	String
4	fn :: loc extract base tag String	String
5	fn :: loc nth str [String] Int String	String
6	fn :: loc replace all loop String String String Int Int Int String	String
7	fn :: loc replace all String String String	String
8	fn :: loc nbsp	String
9	fn :: loc spec es	LocaleSpec
10	fn :: loc spec ca	LocaleSpec
11	fn :: loc spec eu	LocaleSpec
12	fn :: loc spec gl	LocaleSpec
13	fn :: loc spec pt	LocaleSpec
14	fn :: loc spec sv	LocaleSpec
15	fn :: loc spec en	LocaleSpec
16	fn :: loc spec it	LocaleSpec
17	fn :: supported locales	[String]
18	fn :: default locales	[LocaleSpec]
19	fn :: register locale LocaleSpec [LocaleSpec]	[LocaleSpec]
20	fn :: loc spec code LocaleSpec	String
21	fn :: loc spec autonym LocaleSpec	String
22	fn :: loc spec plural rule LocaleSpec	String
23	fn :: loc spec group sep LocaleSpec	String
24	fn :: loc spec dec sep LocaleSpec	String
25	fn :: loc spec months wide LocaleSpec	[String]
26	fn :: loc spec months short LocaleSpec	[String]
27	fn :: loc spec weekdays wide LocaleSpec	[String]
28	fn :: loc spec weekdays short LocaleSpec	[String]
29	fn :: loc spec date patterns LocaleSpec	LocaleDatePatterns
30	fn :: loc find in registry [LocaleSpec] String	LocaleSpec
31	fn :: loc lookup base with [LocaleSpec] String	LocaleSpec
32	fn :: lookup locale with [LocaleSpec] String	LocaleSpec
33	fn :: loc lookup base String	LocaleSpec
34	fn :: lookup locale String	LocaleSpec
35	fn :: normalize locale String	String
36	fn :: language name String	String
37	fn :: loc abs int Int	Int
38	fn :: loc eval plural an String Int Bool	String
39	fn :: loc eval plural rule String Int Bool	String
40	fn :: loc categories for rule String Bool	[String]
41	fn :: plural category String Int	String
42	fn :: plural categories String	[String]
43	fn :: plural category cldr String Int	String
44	fn :: plural categories cldr String	[String]
45	fn :: loc cat to index String	Int
46	fn :: plural index String Int	Int
47	fn :: loc floor div qr Int Int	Int
48	fn :: loc floor div Int Int	Int
49	fn :: loc floor mod r Int Int	Int
50	fn :: loc floor mod Int Int	Int
51	fn :: loc ymd month Int	Int
52	fn :: loc ymd year Int Int	Int
53	fn :: loc days to ymd Int	Int Int Int
54	fn :: loc iso weekday norm Int	Int
55	fn :: loc iso weekday from days Int	Int
56	fn :: loc pad2 Int	String
57	fn :: loc pad4 Int	String
58	fn :: month name String Int	String
59	fn :: month short name String Int	String
60	fn :: loc norm weekday idx Int	Int
61	fn :: loc weekday wide by nw String Int	String
62	fn :: weekday name String Int	String
63	fn :: loc weekday short by nw String Int	String
64	fn :: weekday short name String Int	String
65	fn :: loc ca prep char String Int	String
66	fn :: loc ca prep month String	String
67	fn :: loc eu genitive len String Int	String
68	fn :: loc eu genitive month String	String
69	fn :: loc select date pattern LocaleDatePatterns String	String
70	fn :: loc select dt join LocaleDatePatterns	String
71	fn :: loc render date pattern LocaleSpec String Int Int Int Int	String
72	fn :: format date String String Int	String
73	fn :: loc format time style String Int Int Int	String
74	fn :: format datetime String String Int	String
75	fn :: loc join grouped String String String	String
76	fn :: loc group digits loop String Int String String	String
77	fn :: loc format uint digits String String	String
78	fn :: loc pos int digits Int String	String
79	fn :: loc uint to digits Int	String
80	fn :: loc prepend neg Int String	String
81	fn :: format int String Int	String
82	fn :: loc pow10 Int Int	Int
83	fn :: loc pow10 real Int Real	Real
84	fn :: loc real to int loop Real Int Real Int	Int
85	fn :: loc real to uint Real	Int
86	fn :: loc pad left zeros String Int	String
87	fn :: loc abs float Real	Real
88	fn :: loc sign str float Real	String
89	fn :: loc clamp frac digits Int	Int
90	fn :: loc format decimal scaled String String String Real Int	String
91	fn :: loc format decimal impl String String String Real Int	String
92	fn :: format decimal String Real Int	String

---

42.3. Exploring locale in Depth: Step-by-Step Runnable Examples

42.3.1. Example 1: CLDR Plural Rules (.po-Compatible Mode & Strict CLDR 46 Mode with "many")

fn :: test locale plural rules => ()
      test locale plural rules =
        assert str eq (plural category "es" 1) "one" "AC2: es 1 -> one"
        assert str eq (plural category "es" 0) "other" "AC2: es 0 -> other"
        assert str eq (plural category "es" 5) "other" "AC2: es 5 -> other"
        assert str eq (plural category "es" 1000000) "other" "AC2: es 1000000 default .po -> other"
        assert str eq (plural category "eu" 1) "one" "AC2: eu 1 -> one"
        assert str eq (plural category "eu" 2) "other" "AC2: eu 2 -> other"
        assert str eq (plural category "sv" 1) "one" "AC2: sv 1 -> one"
        assert str eq (plural category "sv" 2) "other" "AC2: sv 2 -> other"
        assert str eq (plural category "ca" 1) "one" "AC2: ca 1 -> one"
        assert str eq (plural category "gl" 1) "one" "AC2: gl 1 -> one"
        assert str eq (plural category "pt" 1) "one" "AC2: pt 1 -> one"
        assert str eq (plural category "en" 1) "one" "AC2: en 1 -> one"
        assert str eq (plural category "zz" 1) "one" "AC2: unknown 1 -> one"
        assert str eq (plural category "zz" 3) "other" "AC2: unknown 3 -> other"

        assert str eq (loc join strs (plural categories "es")) "one,other" "AC2: default plural categories es"
        assert str eq (loc join strs (plural categories "eu")) "one,other" "AC2: default plural categories eu"

        assert int equals (plural index "es" 1) 0 "AC2: plural index 1 -> 0"
        assert int equals (plural index "es" 5) 1 "AC2: plural index 5 -> 1"

        assert str eq (plural category cldr "es" 1000000) "many" "AC2: strict CLDR es 1000000 -> many"
        assert str eq (plural category cldr "ca" 2000000) "many" "AC2: strict CLDR ca 2000000 -> many"
        assert str eq (plural category cldr "pt" 1000000) "many" "AC2: strict CLDR pt 1000000 -> many"
        assert str eq (plural category cldr "es" 0) "other" "AC2: strict CLDR es 0 -> other"
        assert str eq (plural category cldr "eu" 1000000) "other" "AC2: strict CLDR eu 1000000 -> other"
        assert str eq (loc join strs (plural categories cldr "es")) "one,many,other" "AC2: strict CLDR categories es"
        assert str eq (loc join strs (plural categories cldr "sv")) "one,other" "AC2: strict CLDR categories sv"
        ()

42.3.2. Example 2: UTC Date & Datetime Formatting (short, medium, long, full)

fn :: test locale dates and datetimes => ()
      test locale dates and datetimes =
        ts_oct30 = 1793318400
        assert str eq (format date "es" "long" ts_oct30) "30 de octubre de 2026" "AC3: es long date 2026-10-30"
        assert str eq (format date "es" "short" ts_oct30) "30/10/2026" "AC3: es short date"
        assert str eq (format date "es" "medium" ts_oct30) "30 oct 2026" "AC3: es medium date"
        assert str eq (format date "es" "full" ts_oct30) "viernes, 30 de octubre de 2026" "AC3: es full date"

        assert str eq (format date "ca" "long" ts_oct30) "30 d'octubre de 2026" "AC3: ca long date vowel elision d'octubre"
        ts_may15 = 1778803200
        assert str eq (format date "ca" "long" ts_may15) "15 de maig de 2026" "AC3: ca long date consonant de maig"

        assert str eq (format date "eu" "short" ts_oct30) "2026/10/30" "AC3: eu short date Y/M/D"
        assert str eq (format date "eu" "long" ts_oct30) "2026(e)ko urriaren 30a" "AC3: eu long date genitive"
        assert str eq (format date "eu" "full" ts_oct30) "2026(e)ko urriaren 30a, ostirala" "AC3: eu full date"

        assert str eq (format date "gl" "long" ts_oct30) "30 de outubro de 2026" "AC3: gl long date"
        assert str eq (format date "pt" "long" ts_oct30) "30 de outubro de 2026" "AC3: pt long date"
        assert str eq (format date "pt" "full" ts_oct30) "sexta-feira, 30 de outubro de 2026" "AC3: pt full date"

        assert str eq (format date "sv" "short" ts_oct30) "2026-10-30" "AC3: sv short date ISO"
        assert str eq (format date "sv" "long" ts_oct30) "30 oktober 2026" "AC3: sv long date"
        assert str eq (format date "sv" "full" ts_oct30) "fredag 30 oktober 2026" "AC3: sv full date"

        assert str eq (format date "en" "long" ts_oct30) "October 30, 2026" "AC3: en long date"
        assert str eq (format date "en" "full" ts_oct30) "Friday, October 30, 2026" "AC3: en full date"

        assert str eq (format datetime "es" "long" (ts_oct30 + 52245)) "30 de octubre de 2026, 14:30:45" "AC3: es long datetime"
        assert str eq (format datetime "sv" "short" (ts_oct30 + 52245)) "2026-10-30 14:30" "AC3: sv short datetime"

        assert str eq (month name "es" 10) "octubre" "AC3: month name es 10"
        assert str eq (month name "eu" 10) "urria" "AC3: month name eu 10"
        assert str eq (weekday name "es" 5) "viernes" "AC3: weekday name es 5"
        assert str eq (weekday name "sv" 7) "söndag" "AC3: weekday name sv 7"
        assert str eq (weekday name "sv" 0) "söndag" "AC3: weekday name sv 0"
        ()

42.3.3. Example 3: Locale-Aware Integer & Decimal Formatting (format int, format decimal)

fn :: test locale numbers => ()
      test locale numbers =
        nbsp = (char from code 194) + (char from code 160)
        assert str eq (format int "es" 1234567) "1.234.567" "AC4: format int es 1234567"
        assert str eq (format int "ca" 1234567) "1.234.567" "AC4: format int ca 1234567"
        assert str eq (format int "eu" 1234567) "1.234.567" "AC4: format int eu 1234567"
        assert str eq (format int "gl" 1234567) "1.234.567" "AC4: format int gl 1234567"
        assert str eq (format int "pt" 1234567) "1.234.567" "AC4: format int pt 1234567"
        assert str eq (format int "sv" 1234567) ("1" + nbsp + "234" + nbsp + "567") "AC4: format int sv 1234567 with NBSP"
        assert str eq (format int "en" 1234567) "1,234,567" "AC4: format int en 1234567"
        assert str eq (format int "es" (-1234567)) "-1.234.567" "AC4: format int es negative"
        assert str eq (format int "es" 42) "42" "AC4: format int es small"
        assert str eq (format int "es" 0) "0" "AC4: format int es zero"

        assert str eq (format decimal "es" 1234567.89 2) "1.234.567,89" "AC4: format decimal es"
        assert str eq (format decimal "sv" 1234.5 2) ("1" + nbsp + "234,50") "AC4: format decimal sv"
        assert str eq (format decimal "en" 1234.5 2) "1,234.50" "AC4: format decimal en"
        assert str eq (format decimal "es" (-19.99) 2) "-19,99" "AC4: format decimal negative"
        ()

42.3.4. Example 4: Native Language Autonyms (language name) & Tag Normalization

fn :: test locale autonyms normalization and registry => ()
      test locale autonyms normalization and registry =
        assert str eq (loc join strs (supported locales)) "es,ca,eu,gl,pt,sv,en" "AC1: supported locales order"
        assert str eq (language name "es") "Español" "AC1: language name es"
        assert str eq (language name "ca") "Català" "AC1: language name ca"
        assert str eq (language name "eu") "Euskara" "AC1: language name eu"
        assert str eq (language name "gl") "Galego" "AC1: language name gl"
        assert str eq (language name "pt") "Português" "AC1: language name pt"
        assert str eq (language name "sv") "Svenska" "AC1: language name sv"
        assert str eq (language name "en") "English" "AC1: language name en"
        assert str eq (language name "unknown") "English" "AC1: unknown locale falls back to English"
        assert str eq (language name "root") "English" "AC1: root locale falls back to English"
        assert str eq (normalize locale "es-ES") "es" "AC1: normalize locale es-ES"
        assert str eq (normalize locale "CA_ES.UTF-8") "ca" "AC1: normalize locale CA_ES.UTF-8"
        assert str eq (normalize locale "pt-BR") "pt" "AC1: normalize locale pt-BR"
        assert str eq (normalize locale "xx-YY") "en" "AC1: normalize unknown locale to en"

        fr_spec = LocaleSpec "fr" "Français" "one_zero_one" " " "," ["janvier"] ["janv."] ["lundi"] ["lun."] (LocaleDatePatterns "%DD/%MM/%YYYY" "%D %MMM %YYYY" "%D %MMMM %YYYY" "%EEEE %D %MMMM %YYYY" " ")
        reg2 = register locale fr_spec (default locales)
        found_fr = lookup locale with reg2 "fr-FR"
        assert str eq (loc spec autonym found_fr) "Français" "AC1: data-only LocaleSpec registration and lookup"
        ()

---

42.5. Algorithmic Guarantees and RMM1/RMM2 Memory

• Algorithmic & safety guarantee: 100% pure functions with zero global mutable locale state, $O(1)$ proleptic Gregorian UTC calendar conversion, and deterministic fallback to "en".
• Continuous verification: Verified by src/test/ridgun/test locale.rg.